ISSN Printed: 0034-7744 ISSN digital: 2215-2075

Morphometry and meristics of two species of (Siluriformes: ), native of ,

Gorgonio Ruiz-Campos1*, Alejandro Varela-Romero2, David Ceseña-Gallegos1, Carlos Alonso Ballesteros-Córdova1,2 & Sergio Sánchez-Gonzáles3 1. Colección Ictiológica, Facultad de Ciencias, Universidad Autónoma de Baja California. Carretera Transpeninsular Ensenada-Tijuana No. 3917, Colonia Playitas, Ensenada, Baja California, México, 22860; [email protected], [email protected], [email protected] 2. Departamento de Investigaciones Científicas y Tecnológicas de la Universidad de , Boulevard Luis Encinas y Rosales s/n, Hermosillo, Sonora, México, 83000; [email protected] 3. Facultad de Biología, Universidad Autónoma de , Culiacán, Sinaloa, México, 80010; [email protected] * Correspondence Received 13-VIII-2019. Corrected 27-II-2020. Accepted 04-III-2020.

ABSTRACT. Introduction: Morphotypes of native of the Ictalurus (Siluriformes: Ictaluridae) are known to occur in allopatry in the northern Sierra Madre Occidental of Mexico, with only the Yaqui catfish () taxonomically described. Recent genetic analysis of these morphotypes has revealed the monophyly of the I. pricei complex, which indicates Ictalurus sp. from the Culiacán River and San Lorenzo River basins as its nearest genetic relative and recognizes as an evolutionarily significant unit the Culiacán River and San Lorenzo River morphotypes. Objective: To compare the meristic and morphometric characteristics of the catfish of the Culiacán River basin with its nearest genetic relative, the Yaqui catfish, in order to determine the presence of distinctive morphological characters that support genetic evidence previously reported for these morphotypes. Methods: Catfish specimens were collected during various field expeditions (1990-2012) to remote sites of the Sierra Madre Occidental and conducted in the Yaqui River and Culiacán River basins with the purpose of morphological comparison. Forty-five morphological characters (40 morphometric and five meristic) were examined in 76 adult specimens – 52 Ictalurus sp. and 24 Ictalurus pricei. Three groups were subject to a discriminant function analysis (DFA), including two Ictalurus sp. groups from the Humaya River and Tamazula River sub-basins, representing the Culiacán River basin, and one I. pricei group representing the Yaqui River basin. The standardized measurements and meristic data of the catfish morphotypes were compared by means of DFA. Results: The DFA revealed 12 characters to be significantly different (P < 0.01) among the groups compared. The morphological characters separating the Ictalurus sp. (Culiacán River basin) from the Yaqui catfish were associated with lower anal, pelvic and pectoral fin ray numbers, shorter head and predorsal lengths, shorter longest lateral and longest dorsal ray lengths and a narrower premaxilar dentary plate; and finally longer distances in Ictalurus sp. for dorsal-fin origin to last anal-fin ray base and dorsal-fin origin to posterior end of the adipose fin base. The standardized coefficients for canonical variables 1 and 2 accounted for 85.6 % and 14.4 % of the total variation, respectively. Conclusions: The distinctive morphological characters of the Ictalurus sp. found in the Culiacán River basin, combined with the known mitochondrial evidence for this morphotype, identify it as an evolutionarily significant unit that requires description as a new species based on taxonomical protocols.

Key words: morphometrics, meristics, Río Culiacán catfish, evolutionarily significant unit, northwestern Mexico.

Ruiz-Campos, G., Varela-Romero, A., Ceseña-Gallegos, D., Ballesteros-Córdova, C.A., & Sánchez-Gonzáles, S. (2020). Morphometry and meristics of two species of Ictalurus (Siluriformes: Ictaluridae), native catfishes of Sierra Madre Occidental, Mexico. Revista de Biología Tropical, 68(2), 479-491.

Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 479 The family Ictaluridae, or North American MATERIAL AND METHODS catfish, contains 51 nominal species, of which 29 and 10 taxa belong to the genera Noturus Study area: The study area includes the and Ictalurus, respectively (Page et al., 2013). Culiacán River and Yaqui River basins in the Several morphotypes of native Ictalurus catfish SMO (Fig. 1), across the states of Durango, are present in the northern Sierra Madre Occi- Sinaloa and Chihuahua. The Culiacán River dental (SMO), Mexico (Hendrickson, 1983; basin provides drainage to a surface area of 2 Varela-Romero, 2007; Varela-Romero, Hen- 19 150 km in the states of Durango, Sinaloa and Chihuahua, along with the Humaya (11 363 drickson, Yepiz-Plascencia, Brooks & Neely, km2) and Tamazula (3 657 km2) sub-basins. For 2011). Of these, only the Yaqui catfish (Icta- the purposes of the present study, we consid- lurus pricei) from the Yaqui, Mayo, Sonora, ered the Humaya and Tamazula sub-basins as Fuerte, and Casas Grandes river basins (Hen- hydrological and physiographically different drickson, Minckley, Miller, Siebert & Minck- in their middle and upper sections, in which ley, 1980; Miller, Minckley, & Norris, 2005) large artificial reservoirs (the Adolfo López has been formally described (Rutter, 1896; Mateos and Sanalona reservoirs, respectively) Miller et al., 2005). have been built for agricultural irrigation in The presence of native catfish in the north- the Culiacán coastal valley. The hot sub-humid ern SMO was first reported by Rutter (1896), climate in the Culiacán River basin is charac- who described a new species from the Yaqui terized by rains in the summer and an annual River basin, Villarius pricei (currently known average temperature of 12-24 °C and annual as Ictalurus pricei), based on specimens cap- mean precipitation above 600 mm (Arriaga et tured in the San Bernardino creek just south al., 2000). The Yaqui River basin comprises of the international border with Arizona, USA. an area of 71 452 km2, providing drainage to Several authors (e.g. Hendrickson et al., 1980; the states of Sonora (74 %) and Chihuahua (21 Miller et al., 2005; Varela-Romero et al., 2011) %) in Mexico, and Arizona, in the USA (5 %) have referred to the presence of at least one (Cruz-Medina & García-Páez, 2008), while its undescribed allopatric species of the genus climate is controlled regionally by means of its Ictalurus inhabiting the drainages south of the latitudinal position, physical size, altitude, and Fuerte River basin. Recently, based on analysis distance to the sea. Most of the basin comprises of mitochondrial DNA of catfish from north- extra-tropical drylands with a band of extra- western México, Ballesteros-Córdova et al. tropical highlands that follow the SMO. The (2015) identified the monophyly of the Yaqui annual mean temperature along the coast and catfish (Ictalurus pricei) complex, including the basin inland is above 25 °C, while this is Ictalurus sp. from the allopatric populations less than 15 °C in the plateau areas (Hendrick- of the Culiacán River and San Lorenzo River son et al., 1980). basins, as its nearest genetic relative. In support of the recently presented genet- Fish sampling: The catfish specimens ic evidence supporting the recognition of the were collected during various field expeditions Ictalurus sp. from the Culiacán River basin as (1990-2012) to remote sites in the SMO, in the an evolutionarily significant unit (Ballesteros- states of Chihuahua, Sinaloa and Durango, with Córdova et al., 2015), we postulate that this access to which made difficult and risky by morphotype might represent a new species the presence of drug traffickers (Fig. 1, Digital based on morphological characters that distin- Appendix 1). Sampling was carried out in two guish it from its nearest genetic relative, the sub-basins of the Culiacán River (the Humaya Yaqui catfish, both of which present an allopat- and Tamazula sub-basins) and one sub-basin of ric distribution in the SMO. the Yaqui River (the Sirupa-Tutuaca sub-basin).

480 Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 Specimens were captured using AC Smith- morphometric analysis comprised 40 somatic Root 15-B POW electrofishing equipment, distances (Fig. 2A, Fig. 2B, Digital Appen- hooks and lines, and cast nets. In the field, dix 2) following Hubbs and Lagler (1958), the recently captured specimens were photo- Bookstein et al. (1985), and Ruiz-Campos, graphed for the description of their live/fresh Lozano-Vilano and García-Ramírez (2009). All coloration, after which fin tissue clips of each linear measurements were made in millimeters specimen were taken and preserved in 95 (mm) along the left side of each specimen % non-denatured ethanol. All the specimens using a digital caliper (precision, 0.01 mm) were fixed in 10 % formalin, preserved in 70 connected to a PC. % ethanol, and finally donated to the fish col- A scatterplot was used to perform an lections of the Universidad Autónoma de Baja exploratory analysis of the relationship between California (UABC), the Universidad de Sonora the standard length and each morphometric (USON) and the Texas Natural History Collec- character (length and width measurements) tions (TNHC) at the University of Texas. of the examined specimens. This procedure enabled the detection of any aberrant or incon- Morphological comparison: Fifty-two sistent data in the body measurements. Ictalurus sp. specimens (Culiacán River basin, Considering that morphometric variation 66-215 mm standard length [SL]) and 24 Icta- among individuals should be attributable to lurus pricei specimens (Yaqui River basin, body shape differences and not the relative size 186-242 mm SL) were examined for morpho- of the fish, an allometric method (Elliott, Has- metric and meristic comparison. The meristic kard and Koslow, 1995) was used to remove analysis was based on the standardized method size-dependent variation in the morphomet- of Hubbs and Lagler (1958) for the dorsal, anal, ric characters and homogenize their variances caudal, pelvic and pectoral fin-ray counts. The (Jolicoeur, 1963).

Fig. 1. Collecting sites for Ictalurus sp. (1-8) and I. pricei (9, 10) in the Río Culiacán and Río Yaqui basins, respectively, in the Sierra Madre Occidental, Mexico. Numbers indicate the collecting sites as described in Digital Appendix 1.

Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 481 Fig. 2. Morphometric landmarks in specimens of the genus Ictalurus from the Sierra Madre Occidental, Mexico. For a description of landmarks and distances in A and B see Digital Appendix 2.

This allometric method enabled the stan- Tamazula river sub-basins) representing the dardization of the morphometric data by means Culiacán River basin, and one I. pricei group of the equation Ms = Mo (Ls/Lo)b, where: Ms representing the Yaqui River basin. The stan- = standardized measurement; Mo = original dardized measurements and meristic data for length measurement of the character (mm); Ls the catfish groups studied were compared by = overall (arithmetic) mean standard length means of a forward stepwise DFA using Sta- (mm) for all individuals from all populations tistica 6.0 (StatSoft, Inc., Tulsa, OK, 2002). examined; and, Lo = standard length (mm) A step-by-step discrimination model is built of specimen. Parameter b was estimated for in this type of analysis, which, at each step, each character from the observed data using reviews all variables and identifies those which the non-linear equation, M = a Lb, where: M contribute most to the discrimination between = the estimated measurement of the character; groups. parameters a and b are the intercept and slope, The statistical significance of the discrim- respectively; and, L= standard length of the ination among populations was determined specimen (mm). Parameter b was estimated as using Wilk’s lambda (λ), which oscillates the slope of the regression log Mo on log Lt, from 0.0 (perfect discrimination power) to using all fish. 1.0 (absence of discrimination power). The Three groups were considered in the standardized coefficients of the canonical vari- DFA, two Ictalurus sp. groups (Humaya and ables were determined in order to estimate the

482 Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 contribution of each variable in each canonical fin (P < 0.001), number of pelvic rays (P < function; therefore, the value of each coef- 0.001), distance from the orbit to the upper ficient indicates the power of the variables operculum opening (P < 0.001), number of considered in the analysis to either separate pectoral rays (P < 0.01) and interorbital width or discriminate. (P < 0.05; Table 1). The standardized coefficients were plotted Analysis of the standardized coefficients on a Cartesian coordinate system, where their for canonical variables revealed that canonical position and orientation (vectors) indicated roots 1 and 2 explained 85.6 and 14.4 % of the the degree of association between each vari- observed total variation, respectively (Table 2). able and the groups (Pires-Da Silva, Imhoff, For Canonical Root 1, four variables exert- Giarola & Tormena, 2001). Finally, to illustrate ed the major effects: body depth at origin of the separations and relationships among the anal fin origin (Y = -1.08698); distance from populations compared, we built tree diagrams orbit to the upper operculum opening (Y = based on the squared Mahalanobis distances of -1.04841); number of anal rays (Y = -0.73818); the morphological characters examined. and, number of pelvic rays (Y = -0.62839). For Canonical Root 2, two variables exerted RESULTS the major effects, namely the length of dor- sal and pectoral spines (Y = -1.05172 and From the morphological comparison 0.96372, respectively). between Ictalurus sp. specimens from the The highest squared Mahalanobis distance Culiacán River basin (considering the Huma- (59.10) was registered between the Humaya ya and Tamazula river sub-basins separately) River sub-basin and the Yaqui River basin, and Ictalurus pricei specimens from the Yaqui while the lowest (15.76) was between the River basin, 27 of 45 the morphological Humaya River and Tamazula River sub-basins. variables examined entered into the forward The Tamazula River sub-basin and the Yaqui stepwise DFA. The global Wilks lambda (λ) River basin recorded a distance of 39.60. The was 0.02701 (P < 0.0001), indicating a high tree diagram resulting from the squared Maha- degree of discrimination among the groups lanobis distances (Fig. 3A) indicates a high compared. The five most significant vari- degree of discrimination between the Ictalurus ables included body depth at origin of anal sp. specimens from the Humaya River and

TABLE 1 Lambda values of Wilks (p) and tolerance for 10 somatic variables (P ≤ 0.05) in the forward stepwise discriminant function analysis for Ictalurus sp. of the Río Culiacán basin (Río Humaya and Río Tamazula sub-basins) and I. pricei of the Río Yaqui basin, in northwestern Mexico

Variable Wilks Partial F-remove P-level Number of anal rays 0.032422 0.832940 4.713308 0.0136 Number of pectoral rays 0.033093 0.816069 5.296575 0.0084 Orbit to upper opercul opening 0.036523 0.739425 8.281441 0.0008 Dorsal spine length 0.032346 0.834901 4.647038 0.0144 Number of pelvic rays 0.036694 0.735977 8.43033 0.0007 Orbit length 0.032235 0.837783 4.550237 0.0156 Interorbital width 0.032578 0.828954 4.848997 0.0122 Body depth (at anal fin origin) 0.037003 0.729829 8.699308 0.0006 Pelvic fin origin to anal fin origin 0.031090 0.868643 3.553706 0.0365 Width of premaxillar dentary plate 0.030874 0.874715 3.365901 0.0430

Number of variables in the model: 27; Wilks Lambda: 0.02701; approx. F(54, 94) = 8.8519, P < 0.0001.

Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 483 TABLE 2 Standardized coefficients for canonical variables resulting from the discriminant function analysis of morphological data in Ictalurus sp. of the Río Culiacán basin (n = 52) and I. pricei of the Río Yaqui basin (n = 24), in the Sierra Madre Occidental, Mexico

Variable Root 1 Root 2 Number of anal rays -0.73818 0.25144 Number of pectoral rays -0.47715 -0.61656 Longest maxilar barbel length -0.32428 -0.61145 Orbit to upper opercule opening -1.04841 -0.25635 Length of caudal middle rays (from hypural plate) 0.33992 -0.26116 Dorsal spine length -0.13743 -1.05172 Longest lateral barbel length -0.05913 0.59828 origin to pectoral fin origin 0.30900 -0.3084 Number of pelvic rays -0.62839 0.58116 Orbital length 0.13826 -0.70431 Pectoral spine length 0.05883 0.96372 Longest nasal barbel length 0.23043 0.22421 Interorbital width 0.54342 -0.84529 Pectoral fin origin to pelvic fin origin 0.19634 -0.36921 Mouth width -0.34814 0.58001 Body depth (at anal fin origin) -1.08698 -0.31499 Head width (at opercules) 0.55541 -0.19311 Pelvic fin origin to anal fin origin -0.5702 0.04686 Width of premaxilar dentary plate -0.58649 -0.22642 Predorsal length 0.21914 0.53912 Caudal peduncle depth 0.48098 0.32647 Length of penultimate anal ray -0.26833 -0.13646 Pelvic fin origin to posterior connection of adipose fin 0.49138 -0.19764 Snout width (at maxilla) 0.58904 0.06044 Anal fin base length -0.42307 0.36902 Caudal peduncle length -0.34173 0.41168 Adipose fin base to caudal fin 0.12610 -0.39151 Eigenval 11.56908 1.94604 Cum. Prop. 0.856010 1.00000

Variables exerting major contributions to the observed total variation are depicted in bold.

Tamazula River sub-basins (Culiacán River individual from the Tamazula River population basin) and the I. pricei specimens from the was classified incorrectly into the Humaya Yaqui River basin. The Ictalurus sp. specimens River population. In the scatterplot graph for from the two sub-basins of the Culiacán River roots 1 and 2 (Fig. 3B), the populations of the revealed a high similarity level, with a value of Humaya River and Tamazula River sub-basins 84.2 % (Fig. 3A). appear as juxtaposed groups, while the popula- The percentage of correct classification, by tion from the Yaqui River basin is widely sepa- means of the DFA, of individuals in the exam- rated from both populations of the sub-basins ined groups was 98.7 %, indicating that almost of the Culiacán River. all individuals across the different drainages Morphologically, the Culiacán River cat- were correctly classified into their respective fish differs from the Yaqui catfish by means groups (see scatterplots in Fig. 3B). Only one of the following characters: a lower number of

484 Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 Fig. 3. (A) Tree diagram derived from the squared Mahalanobis’ distances and (B) scatter plot of centroids for roots 1 and 2 in Ictalurus sp. from the Río Culiacán basin (Río Humaya and Río Tamazula sub-basins) and I. pricei from the Río Yaqui basin, in the Sierra Madre Occidental, Mexico.

Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 485 Fig. 4. Mean and 95 % confidence interval of the 10 most significant morphological characters that separate Ictalurus sp. of the Río Culiacán basin (Río Humaya and Río Tamazula sub-basins) from Ictalurus pricei of the Río Yaqui basin, Sierra Madre Occidental, Mexico.

486 Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 anal (Fig. 4A), pelvic (Fig. 4B) and pectoral fin lobes are rounded (Fig. 5A, Fig. 5B) while fin rays (Fig. 4C); smaller dimensions for head those of the Yaqui catfish are pointed (Fig. 5C). length (Fig. 4D) and predorsal length (Fig. 4E); The body coloration of fresh catfish speci- shorter longest lateral barbel length (Fig. 4F); mens from the stream El Rodeo, a tributary of shorter longest dorsal ray length (Fig. 4G); the Tamazula River sub-basin (Culiacán River narrower premaxilar dentary plate (Fig. 4H); basin), collected on 19 February 2011 (Fig. larger distance from dorsal fin origin to last 5A), is dark gray on the head and dorsum, anal ray base (Fig. 4I); larger distance from while the medium gray to yellowish brown dorsal fin origin to posterior end of the adipose observed on the sides contrasts with the shiny fin base (Fig. 4J); and, finally, the tips of caudal white observed on the belly. Fresh catfish

Fig. 5. Life coloration of native catfishes of the genus Ictalurus from the Sierra Madre Occidental, Mexico. (A) Ictalurus sp., Arroyo El Rodeo [Río Tamazula sub-basin], Durango; (B) Ictalurus sp., Arroyo Surutato [Río Humaya sub-basin], Sinaloa; and (C) Ictalurus pricei, Río Fuerte basin, Sinaloa. Photographs by S. Sánchez-Gonzáles (A and B) and A. Varela-Romero (C).

Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 487 specimens from the stream Surutato, a tribu- Recently, molecular evidence based on tary of the Humaya River sub-basin (Culiacán cytochrome b (Varela-Romero, 2007; Varela- River basin), captured on 29 February 2012 Romero, Ballesteros-Córdova, Ruiz-Campos, (Fig. 5B), presented the following: a dark blue Sánchez-Gonzáles, & Brooks, in press), the gray coloration on the head and dorsum which cytochrome oxidase subunit 1 (Castañeda- contrasts with the clear blue gray observed on Rivera, Grijalva-Chon, Gutiérrez-Millán, Ruiz- the sides; small black spots are dispersed along Campos, & Varela-Romero et al., 2014) and the the sides of the body and are more conspicu- sequencing of four geographical mitogenome ous on small individuals; white mental barbels haplotypes of Yaqui catfish and Sinaloan cat- contrast with the dark gray coloration of the fish (Culiacán River and San Lorenzo River maxillary barbels; and, all fins are dark gray. basins) has placed the geographical haplotypes The fresh coloration of Ictalurus pricei (Fig. of I. pricei within a clade of specific identity. 5C) was clear brown on the head, dorsum and This identity is close to Sinaloan catfish hap- sides, while all fins had a clear gray tonality, lotypes, thus supporting the hypothesis that and the caudal fin had a black edge. Sinaloan catfish are a distinct evolutionary unit (Ballesteros-Córdova et al., 2015). DISCUSSION The discriminant function analysis applied, in the present study, on Ictalurus sp. from the The Mexican highlands are considered a Culiacán River basin (Humaya and Tamazula focus of biodiversity in North America (Rama- sub-basins) and I. pricei from the Yaqui River moorthy, Bye, Lot, & Fa, 1993; Bye, 1995), basin enabled the identification of a set of containing highly endemic flora and fauna diagnostic morphological characters that can be as a result of the strong role played by diver- used to distinguish them. The Culiacán River gence and speciation (MacCormak, Peterson, catfish (both sub-basins) is distinguished from Bonaccorso, & Smith, 2008; Schönhuth et al., the Yaqui River catfish by: its smaller aver- 2011). In the historical context of the SMO, age size (140 mm SL vs. 212 mm SL); lower the geographic isolation among hydrological number of anal (≤ 19 vs. ≥ 23), pelvic (≤ 7 vs. drainages has facilitated reproductive isolation 8), and pectoral (7 vs. 10) fin rays; smaller and morphological divergence, resulting in the dimensions for head length, predorsal length, formation of unique phenotypes (sensu Wor- longest lateral barbel length, longest dorsal ray sham, Julius, Nice, Diaz, & Huffman, 2017). length and premaxilar dentary plate width; and, The geographical isolation of the Culiacán finally, larger distances in Ictalurus sp. (Culi- River catfish and its consequent differentiation acán River basin) from dorsal fin origin to last (Varela-Romero et al., 2011) could be related anal ray base, and dorsal fin origin to posterior to various orographic events and episodic end of the adipose fin base. aridity during the Miocene which, combined The morphological characters described with pluvial cycles in the Pleistocene, resulted above support the hypothesis of the present in the separation of the different hydrological study, which stipulates that the Ictalurus sp. drainages in the SMO (Schönhuth, Doadrio, & of the Culiacán River basin (Humaya and Mayden, 2006; Schönhuth et al., 2011, 2014; Tamazula sub-basins) represents a different Smith et al., 2002). This tectonic-climatic event form to the nominal species Ictalurus pricei has been also proposed as the main causal fac- of the Yaqui River basin, as already confirmed tor of the speciation of other fish genera in the by genetic analysis undertaken using mito- SMO, such as Gila (Schönhuth et al., 2014), chondrial DNA (Ballesteros-Córdova et al., Codoma (Schönhuth, Lozano-Vilano, Perdices, 2015; Castañeda-Rivera et al., 2014; Varela- Espinosa, & Mayden, 2015) and Catostomus Romero, 2007; Varela-Romero et al., 2011; (Ruiz-Campos, Sánchez-Gonzáles, Mayden, & Varela-Romero, et al., in press). In this context, Varela-Romero et al., 2016). the Ictalurus sp. inhabiting the Culiacán River

488 Rev. Biol. Trop. (Int. J. Trop. Biol.) Vol. 68(2): 479-491, June 2020 basin represents an evolutionarily significant con su pariente genético más cercano, el bagre Yaqui, unit (Wiley, 1981) that should be described in con el propósito de determinar la presencia de caracteres the taxonomic standards for future legal protec- morfológicos distintivos en apoyo a evidencia genética previamente reportada para esos morfotipos. Métodos: tion by the Mexican government (Hendrickson Especímenes de bagres fueron recolectados durante varias et al., 2003). Currently, the native catfish expediciones de campo (1990-2012) en sitios remotos de populations of the Culiacán River basin face la Sierra Madre Occidental en las cuencas de los ríos Yaqui several threats from anthropogenic activities, y Culiacán para comparación morfológica. Cuarenta y such as the alteration of their habitat by min- cinco caracteres morfológicos (40 morfométricos y cinco merísticos) fueron examinados en 76 especímenes adultos ing, the diversion or impoundment of flows, (52 de Ictalurus sp. y 24 de Ictalurus pricei). Medidas cor- or the potential introduction of exotic catfish porales estandarizadas y datos merísticos de los morfotipos (Ictalurus punctatus), all of which affect the de bagres estudiados fueron comparados por medio de un population distribution and abundance of this análisis de función discriminante (AFD). Resultados: El native taxon. AFD arrojó 12 caracteres significativamente diferentes (P < 0.01) entre los grupos comparados. Los caracteres morfológicos que distinguen al bagre del río Culiacán ACKNOWLEDGMENTS del bagre Yaqui, estuvieron asociados con un menor número de radios anales, pélvicos y pectorales, así como We thank Héctor M. Inzunza-Beltrán, dimensiones más pequeñas para la longitud de la cabeza, longitud predorsal, longitud de la barbilla lateral más larga, Gonzalo Valdéz-Sánchez, James Brooks and longitud del radio dorsal más largo y una menor anchura Nick Smith for helping in the fish sampling. de la placa dentaria premaxilar; y finalmente, dimensiones Two anonymous reviewers made useful com- mayores en Ictalurus sp. (cuenca del río Culiacán) para ments that substantially improved the clarity of distancias como origen de aleta dorsal a la base del último the manuscript. radio anal y origen de aleta dorsal a conexión posterior de aleta adiposa. Los coeficientes estandarizados para las variables canónicas 1 y 2 explicaron el 85.6 y 14.4 % de Ethical statement: authors declare that la variación total, respectivamente. Conclusiones: Los they all agree with this publication and made caracteres morfológicos distintivos de Ictalurus sp. de la significant contributions; that there is no con- cuenca del río Culiacán, en combinación con la evidencia flict of interest of any kind; and that we fol- mitocondrial conocida para este mismo morfotipo, permite reconocerlo como una unidad evolutivamente significativa lowed all pertinent ethical and legal procedures y que requiere ser descrita como una especie nueva bajo los and requirements. All financial sources are protocolos taxonómicos. fully and clearly stated in the acknowledge- ments section. A signed document has been Palabras clave: morfometría, merística, bagre del río filed in the journal archives. Culiacán, unidad evolutivamente significativa, noroeste de México.

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